Various processes for the purification and liquefaction off helium from a crude helium stream are known in the art.
In U.S. Pat. No. 4,192,661, a cryogenic apparatus is disclosed with an improved flow path for removing impurities introduced by a make-up stream of cryogenic fluid by directing the make-up stream to means to adsorb impurities therein prior to combining the make-up stream with the main feed stream for the cryogenic apparatus.
In a paper from the 6the International Congress of Refrigeration, Washington, D.C., 1971, by Collins and Doherty (Vol I, P95 of the Proceedings), a freeze-out type helium make-up gas purifier is described, and an article by Kneuer et al, Cryogenics, March 1980, (P129), an automatic multi-range helium-liquefaction plant is described.
U.S. Pat. No. 3,331,213 discloses a process for the separation of gaseous mixtures, in particular, a helium-nitrogen mixture using the higher boiling point component liquid to provide refrigeration for the process.
U.S. Pat. No. 3,599,438 discloses a process for the enrichment of a crude helium stream. The refrigeration duty required by the process is provided by an isentropic expansion of the enriched helium stream.
A typical process for purification and liquefaction of helium is shown in FIG. 1. In this process, crude helium feed is purified by a combination of cryogenic separation and non-cryogenic adsorption processes. The final cryogenic separator in the purifier typically supplies an internal liquid nitrogen stream which is rewarmed to recover refrigeration. Refrigeration requirements for the purifier are typically supplied with liquid nitrogen.
The pure helium stream produced by the purification process is then fed to a separate processing unit for liquefaction. Refrigeration for the liquefier is supplied by either expanding high-pressure recycle helium in an expansion engine or a combination of helium expansion and liquid nitrogen.
Liquid nitrogen required for purifier refrigeration, liquefier refrigeration, and other utility uses, is typically produced in a nitrogen liquefier from gaseous nitrogen extracted from the crude helium stream.
The use of separate processing units for each operation results in high capital costs and an energy-intensive process. The small nitrogen expanders used in the nitrogen liquefier are unable to provide refrigeration at high-efficiency levels.
The art as represented above has failed to disclose an efficient manner in which to both purify and liquefy helium from a crude helium feed stream in an integral unit which is energy-efficient yet not capital intensive. The solution to these problems are the objectives of the present invention.